Effects of SCH23390 and raclopride on anxiety-like behavior in rats tested in the black-white box.

Dopamine (DA) systems are activated by stress, and this response has as a corollary the induction of stress-related behaviors such as anxiety. In mice, D2 receptor blockade produces an apparent anxiogenic effect, although locomotor impairments might have been present. We investigated the effects of D1 and D2 antagonists on a variety of anxiety-like behaviors induced by the black-white box in rats and carefully screened for any locomotor deficits. Adult male Lister hooded rats were injected with either the D1 antagonist SCH23390 (0. 0.1. or 0.25 mg/kg i.p.) or the D2 antagonist raclopride (0, 0.05, or 0.10 mg/kg i.p.) 20 min prior to being placed into the white chamber of the black-white box (n = 8-10/group). Rats were videotaped and the tapes were scored for latency to exit the white chamber, latency to reenter the white chamber, time spent in the white chamber, intercompartmental crossing, and locomotor activity. ANOVA revealed no effect of the D1 antagonist SCH23390 on any behavioral measure. However, the raclopride-treated rats left the white area sooner than control rats (p < 0.01). Raclopride-treated rats also exhibited delayed reentry times to the white chamber compared to control rats (p < 0.01) and spent significantly less time in the white chamber (p < 0.05). Neither SCH23390 nor raclopride affected locomotor activity in a manner that confounded these behaviors. These results confirm that D2 receptor blockade enhances anxiety in rats tested in the black-white box.